I couldn't resist and found some more time today so I have another update.
I have added a main menu with level selection, level flow (so completing level 1 automatically loads level 2), sorted out scene management to handle asynchronously loading levels, added animated light sources, improved performance and visuals by actually carrying out rendering at the correct resolution for the pixel art rather than the native resolution of the monitor, and started work on a second level where water is used in place of the mirror as the reflected world you can jump in and out of.
I hope to flesh out the 2nd level a little more tomorrow, still in time for the end of the jam, but am very happy with the advances made today. It is feeling like a "real" game now.